The present invention relates to an optical disc reproducing apparatus which reproduces audio data recorded on an optical disc, and a reproducing method therefore.
As an optical disc on which digital audio data is recorded, CD-DA (Compact Disc-Digital Audio) has been developed. There is recorded on the CD-DA, 16-bit digital audio data with a track pitch of 1.6 μm, obtained by sampling at 44.1 kHz sampling frequency. On the other hand, there has been developed a high-density optical disc, on which 1-bit digital audio data is recorded with a track pitch of 0.74 μm, the data being obtained by sampling at a sampling frequency of 2822.4 kHz and being subjected to delta-sigma modulation (for example, see “About SUPER AUDIO CD”, searched on the Internet URL: http://www.super-audiocd.com/aboutsacd/format.htm1, Mar. 8, 2004).
A hybrid layer disc (hereinafter, referred to as “hybrid disc”) is one type of such high-density optical disc. The hybrid disc includes two types of recording layers, i.e., a recording layer (hereinafter, referred to as “HD (High Definition) layer”) on which 1-bit digital audio data obtained by sampling at 2822.4 kHz and subjected to delta-sigma modulation is recorded, and a recording layer (hereinafter, referred to as “CD layer”) on which 16-bit digital audio data obtained by sampling at 44.1 kHz is recorded. In addition, a single layer disc having only one HD layer, and a dual-layer disc having two levels of HD layers are also categorized as high-density optical disc. Any of those optical discs has a shape identical to that of CD (Compact Disc).
In an optical disc with such a high recording density, the HD layer has a two-channel stereo area where two-channel digital audio data is recorded, and a multi-channel area where digital audio data of multi channels up to six channels is recorded. Data items recorded in the respective areas have basically the same contents.
Furthermore, in the hybrid disc, two-channel audio data including the same contents, which is reproducible by a general CD player, is recorded in the CD layer. An optical disc reproducing apparatus which is capable of reproducing data on such hybrid disc as described above, reads out data recorded in the HD layer and data recorded in the CD layer, by varying a wavelength of the laser beam irradiated from an optical pickup and an aperture ratio of objective lens.